In general, multilayer silver halide color photographic elements are processed by a color development step and a desilvering step after imagewise light exposure. In the color developing step, the imagewise exposed silver halides contained in the photographic element are reduced to metallic silver and at the same time the oxidized color developing agent contained in the color developer solution reacts with color forming couplers in the color photographic element to form dye images in the element. In the subsequent bleaching step, metallic silver thus formed is oxidized by a bleaching agent contained in the bleach solution, and the silver ion derived from bleaching, as well as the unexposed and undeveloped silver halide, are converted into a soluble silver complex by the action of a fixing agent contained in the fixing solution during the fixing step and dissolved away. Alternatively, the bleaching agent and the fixing agent can be combined in a bleach-fixing solution and the silver removed in one step by the use of such a solution.
Recently in this field, it has been found desirable to shorten the time required for photographic processing, in particular to shorten the post development desilvering step which consumes more than half of the overall processing time. However, juxtaposed with this trend to shorten processing time there is the problem that commercial bleaching solutions become generally less effective during use than initial fresh compositions. In particular, the effectiveness of the bleach solution is degraded by the carryover of the developer solution into the bleach solution, resulting in dilution and an increase of pH of the bleach solution. When bleaching time is shortened and effectiveness of the bleach bath is diminished, metallic silver retention occurs in the processed photographic element and quality of the resulting photographic image is reduced.
As a method of increasing the bleaching power and improving desilvering property, the use in photographic elements of bleach accelerating releasing (BAR) couplers is described, for example, in Research Disclosure 11449, JP 55-29805, U.S. Pat. No. 4,293,691, Research Disclosure 24241 and EP 193,389. The BAR couplers contain in the active coupling position a bleach accelerator moiety which is released during processing of the photographic element. Preferred bleach accelerator moieties are aliphatic and heterocyclic thiols.
Typically, multilayer silver halide color photographic elements comprise a support having coated thereon at least two red sensitive silver halide emulsion layers, at least two green sensitive silver halide emulsion layers, a yellow filter layer, and at least two blue sensitive silver halide emulsion layers. Since a satisfactory silver removal is required even when the silver is in a condition difficult for removal such as in the undermost silver halide layers (the ones nearest the support), BAR couplers are usually incorporated in the red sensitive silver halide emulsion layers.
EP 456,181 discloses multilayer color photographic elements including a unit of three adjacent red sensitive silver halide emulsion layers having a first red sensitive layer farthest from the support being more sensitive than a second or mid red sensitive layer which is more sensitive than a third red sensitive layer closest to the support. The examples disclose specifically use of BAR couplers in the most sensitive layer of the triple-coated unit. The same is also disclosed in JP 02-113,242 and U.S. Pat. No. 4,865,959.
However, it has been found that the incorporation of BAR couplers to ensure adequate bleachability can have pronounced side effects on the sensitometric and color reproduction performance of the multilayer photographic element when the element containing the BAR coupler is processed in the desilvering step to reduce residual silver.
Therefore, there is a need for a multilayer color photographic silver halide element which enables improved silver bleaching and produces images having improved color reproduction.